Thermoplastic resins are typically formed by extruding the material through a through a die which shapes the material into long strands. The raw material is placed in a hopper where it is moved into and through a chamber by a screw. The mechanical action of the feeder screw heats and feeds the material through chamber which is typically in the shape of a barrel. The heated and compressed material is then forced through the die at the discharge end of the extruder to form the strands.
The extruded strands are cooled and then chopped into pellets. Typically, the pellet size is on the order of one eighth inch in length by a eighth inch in diameter. The resulting pellets are collected and typically stored. The stored pellets are transported through conduits for packaging in bags or boxes for shipment. Also, the pellets are often transported from the bags or boxes through a transfer system to extrusion equipment for molding into the shape of the final article.
Transfer of solid material is critical to many operations. A weak point in every transfer system is corners where the material changes direction and impinges upon the transfer line. The impingement causes wear at the at the curved areas, i.e. at the elbows. As wear continues an opening will develop and lead to loss of material and shut down of processes dependent on continuous feed of solid materials such as extrusion or injection molding, etc. A catastrophic failure of an elbow can result in even more loss of material and loss time.
There are problems associated with various standard elbow designs and materials. Curved glass for instance is thinned on the outer curve and due to is brittle nature it may be punctured resulting in catastrophic failure. A single chunk of metal or stone can break a whole series of glass elbows. Stainless steel may be used, but it will wear through and may cause contamination of the transferred material with metal. Metal contamination is a problem where good electrical properties are needed such as in plastic electrical connectors. Stainless steel has been treated to give a hardened surface by processes such as nitriding, but this only hardens the outer surface leaving the interior of the elbow to erode.
Elbows made of alumina cannot be readily joined to each other. Typically, such elbows are encased in a large concrete metal sleeve for, joining, protection and support. The resulting constructions are heavy and bulky. They may require support and often need clearance not available in many installations.
U.S. Pat. No. 4,199,010 to McGuth relates to a conduit used to convey particulate matter in which erosion is diminished. A liner placed within the outer wall of the conduit is of ceramic material which is highly resistant to erosion. U.S. Pat. No. 4,684,155 describes a pipe elbow with an abrasion resistant composite inner liner. U.S. Pat. No. 4,478,253 describes an erosion resistant elbow for solids conveyance using a concentric layer. The above elbows are of complex construction and use various wear resistant and supporting layers to form a composite type construction for an elbow.
Hence, it is desirable, to have an elbow for transferring particulate with wear resistant properties that will not fail catastrophically and that is of simple construction.